Fluid filter

ABSTRACT

The present invention deals broadly with the field of fluid filtration. More specifically, however, the invention deals with a fluid filter wherein the filter medium is automatically purged of particulate contaminants each time fluid under pressure is initially introduced through an inlet port to the filter. A preferred embodiment of the invention is particularly appropriate for use with systems such as water systems wherein constant pressure can be provided to the system even when contaminants are purged from the filter housing.

TECHNICAL FIELD

The present invention deals broadly with the field of fluid filtration.More specifically, however, the invention deals with a fluid filterwherein the filter medium is automatically purged of particulatecontaminants each time fluid under pressure is initially introducedthrough an inlet port to the filter. A preferred embodiment of theinvention is particularly appropriate for use with systems such as watersystems wherein constant pressure can be provided to the system evenwhen contaminants are purged from the filter housing.

BACKGROUND OF THE INVENTION

Various types of filtration devices are known and employed in the filterindustry. Canister-type filters are, typically, used for removingparticulate matter from lubricating oils in vehicles and othermachinery. Such filters are attached to the vehicle or machine tocontinuously filter the oil while the machine is operating.

Canister-type filters which are used on motor vehicle engines, whilebeing able to operate satisfactorily for a period of time, loseefficiency as time passes and particulate matter builds up on the filtermedium. They must, therefore, be discarded and replaced afterapproximately 100 to 300 hours of use.

Canister-type filters can also be employed for filtration of particulatematter from water. Such filters can be used in homes and industry forremoving sand, grit, rust, and water treatment chemicals from watersupplies. Use of such filters is particularly appropriate in rural homeswhere the water supply has a high concentrate of particulate deposits.

Again, however, the useful life of the filter is limited by the rate atwhich clogging occurs. As clogging increases, the pressure drop acrossthe filter medium increases commensurately.

A significant problem in the filtration industry has, therefore, beenthis residual build-up of filtered particulates on the filter medium.Because of the typical surface area of filtration medium elements,little storage capacity is afforded. A relatively short component life,thereby, results.

One solution which has been attempted and which has gone far toresolving these problems is a self-cleaning fluid filter as disclosed inApplicant's prior patent, U.S. Pat. No. 4,645,591, which issued on Feb.24, 1987. The device of that document, while being able to filtervarious fluids, was particularly intended for use in vehicle lubricationsystem filtration. Tne canister housing of the filter device disclosedin that document employed means for mating the filter with a nipple onthe face of the engine with which it is intended to be used.

As previously indicated, that invention was a significant advance overthe prior art. The housing defined a sump into which particulatebuild-up on the filter medium, purged during initial start-up of theengine, was deposited. Consequently, the problem of the limited surfacearea of the filter medium was overcome. This, in turn, extended the useof the filter.

Still, however, the life of the filter was limited, although to a lesserextend than in prior art devices, because of the limited capacity of thesump. While the presence of the sump significantly multiplies usefullife of a device constructed in accordance with that patent, eventually,the sump becomes filled, and the filter canister must be discarded.

Additionally, the particular design employed in the device illustratedin that patent was relatively complicated in operation. Further, thefilter illustrated in that document provided certain safeguards whichare, typically, necessary in a filtration system such as in a motorvehicle. In a constant pressure system, such as a water supply of amunicipality, certain of those safeguards are unnecessary.

The present invention is an improvement over prior art filters includingApplicant's invention as disclosed in his U.S. Pat. No. 4,645,591. Itprovides a filtration mechanism which is simple in both its constructionand operation. Additionally, however, it provides a filter which has avirtually unlimited operational life.

SUMMARY OF THE INVENTION

The present invention is a self-cleaning fluid filter which includes ahousing. One wall of the housing has both fluid inlet and outlet portsformed therein. These ports are to afford ingress and egress,respectively, of a pressurized fluid.

A first sleeve is disposed within the housing and extends from the wallin which the inlet and outlet ports are commonly formed. The sleeve hasan interior chamber which is in fluid communication with the outletport. The sleeve comprises two sections: a narrowed portion immediatelyproximate the outlet port, and an expanded port which is remote from theoutlet port. The narrowed portion is provided with at least one orificeformed therein.

The filter further includes a second sleeve which also extends from thecommon wall of the housing. The second sleeve generally concentricallyencircles an axial length of the narrowed portion of the first sleeve.An annular space, in fluid communication with the inlet port filter, is,thereby, defined between the first and second sleeves. The second sleevehas a distal end which is spaced axially from the common wall toward theexpanded portion of the first sleeve.

A generally cylindrical filter cartridge is received within the housingto encircle the expanded portion of the first sleeve. The filtercartridge is disposed for telescoping movement relative to that expandedportion of the first sleeve. Movement of the filter cartridge occurs inresponse to the introduction and termination of flow of the pressurizedfluid through the inlet port. An end of the filter cartridge mostclosely proximate the wall in which the inlet port is formed carries apiston. The piston is, when the filter cartridge is in a primaryposition thereof, received witnin the annular space and occludes flow offluid being introduced to the filter, through the inlet port, beyond thepiston. The fluid, however, drives the piston away from the wall inwhich the inlet port is formed to urge the filter cartridge to asecondary position, wherein the piston has exited the annular space andis disposed axially between the distal end of the second sleeve and theorifice or orifices formed in the narrowed portion of the first sleeve.

Means, such as a coil spring, are provided for biasing the filtercartridge to its primary position wherein the piston carried by thecartridge occludes fluid flow through the annular space and away fromthe wall in which the inlet port is formed. The normal, primary positionof the cartridge is one wherein the piston carried thereby is receivedwithin the annular space between the first and second sleeves.

The filter includes a valve member which is received within the narrowedportion of the first sleeve. In a preferred embodiment, the valve memberis sleeve-like in construction.

The valve member is disposed within the narrowed portion of the firstsleeve for reciprocal movement relative thereto. The valve member isdisposed for movement between a primary position, wherein the valvemember occludes the orifice or orifices formed in the first sleeve, anda secondary position, spaced axially from the primary position of themember, wherein the orifice or orifices are unobstructed.

Finally, the invention includes means for urging the valve memberbetween its primary and secondary positions. The valve member normallyoccupies its primary position, and the urging means urge the valvemember to its secondary position as fluid flow is introduced through theinlet port and the filter cartridge is moved from its primary positionto its secondary position. The urging means, further, urges the valvemember from its secondary position, wherein the orifice or orifices areunobstructed, back to its primary position as fluid flow through theinlet port is discontinued to allow the filter cartridge biasing meansto urge the filter cartridge from its secondary position back to itsprimary position.

In the preferred embodiment, the valve member urging means comprises avalve piston received within the expanded portion of the first sleeve.The valve piston is operatively connected to the valve member so that,as the piston is reciprocated within the expanded portion of the firstsleeve, the valve member will be reciprocated commensurately within thenarrowed portion of the first sleeve.

As fluid is introduced through the inlet port into the annular space,the piston carried by the filter cartridge is driven away from the wallin which the inlet port is formed and past the distal end of the secondsleeve. The valve piston then becomes exposed to pressure from the fluidentering the inlet port. As pressure is brought to bear upon the valvepiston, it will be driven axially to drive, in turn, the valve memberaxially away from its position occluding the orifice or orifices in thefirst sleeve narrowed portion.

When fluid flow through the inlet port is terminated, the cartridgemember will return to its primary position, and pressure will not becontinuously exerted upon the piston received within the expandedportion of the first sleeve. Biasing means can be provided to engageeither the valve member or the piston operatively connected to the valvemember. When pressure on the piston connected to the valve member isterminated, the valve member will, therefore, be returned to its primaryposition occluding the orifice or orifices in the first sleeve.

The preferred embodiment of the invention also includes structurewhereby a sump within the housing can be purged, at intervals, ofparticulate matter which has been scoured from the surface of the filtermedium carried by the filter cartridge. The purging means comprises ascavenger valve having a spool member disposed for reciprocation througha scavenger port. The spool is operatively connected to the valve memberand moves reciprocally therewith.

When the valve member is in its primary position, the spool is disposedso that a primary, annular land thereof is in a position occluding thescavenger port in the housing. As the valve member, however, is urgedtoward its secondary position, a reduced diameter portion of the spoolis axially coextensive with the scavenger port, the primary land havingbecome unseated. With the spool in this position as the valve membertransits to its second position, fluid in the sump and particulatematter carried thereby are purged from the filter housing.

As operation of the filter is continued, a secondary annular landbecomes axially coextensive with the scavenger port. This land, as inthe case of the primary land, has a diameter and sealing means so that,when it is so axially coextensive with a scavenger port, it precludesflow therethrough. As will be able to be seen then, in view of thisdisclosure, as the spool is drawn reciprocally by the valve member,purging of the sump will be occasioned only during the transit of thespool as the valve member moves between its primary and secondarypositions. During both a static status and full operation of the filter,the scavenger port will be occluded, and purging of fluid therethroughwill be precluded.

The present invention is thus an improved self-cleaning fluid filter.More specific features and advantages obtained in those features willbecome apparent with reference to the DETAILED DESCRIPTION OF THEINVENTION, appended claims, and accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional, side elevational view of the present inventionwith the disposition of the parts illustrated as during a static status;and

FIG. 2 is a view similar to FIG. 1 but illustrating the variouscomponents in the positions they occupy during full operation of thefilter.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings wherein like reference numerals denotelike elements throughout the several views, the figures illustrate afilter 10 in accordance with the present invention. The filter 10, asshown, employs a generally circularly cylindrical canister housing 12which encloses the various operational components. While not essentialto the operation of the invention, the filter 10 would typically beoriented as shown in the figures. That is, an end of the filter 10including inlet and outlet ports 14, 16 would be disposed at the top.Further definition of the invention will, therefore, be made withreference to this orientation.

The filter housing 12 is further defined by an upper closure wall 18having the inlet and outlet ports 14, 16 formed therein, and a lowerconical wall 20 having a scavenger port 22 formed therein. The scavengerport 22 provides fluid communication between a sump 24 in the lowersection of the housing 12 and a conduit 26 leading to a drain (notshown).

The upper closure wall 18 of the housing 12 can be integrally formedwith a fitting 28, generally disk-like in configuration, which providespassage for fluid to be introduced into the filter 10 and be evacuatedtherefrom.

The disk-like member 28 is shown as including a generally radiallyextending passage 30 which is in fluid communication with the inlet port14. The passage 30 is, at its radially outward end (as at 32),internally threaded so that it can be mated witn a hose or tube (notsnown) providing the source of fluid to be filtered.

Similarly, a passage 34 extending radially in an opposite direction isin fluid communication with the outlet port 16. This passage 34 providesfluid flow from the outlet port 16 to a hose or other type of conduit towhich the fluid is to be channelled. Again, a radially outward end ofthe passage (as at 36) can be internally threaded to afford matingfacility.

An assembly of the upper closure wall 18 of the housing 12 and thedisk-like member 28 can be provided with threads 38 so that the assemblycan be tightened onto the cylindrical side wall 40 of the housing 12.Corresponding external threads 42 on the outer surface of thecylindrical housing wall 40 would, of course, be provided. An O-ringseal 44 can be received within a recess 46 in the assembly to provide aseal between the side cylindrical wall 40 of the housing 12 and theassembly.

A first sleeve 48 is shown as extending downwardly from the upper wall18 of the housing 12. The first sleeve 48 is shown as being alignedalong an axis 50 of the housing 12, and it is in fluid communicationwith the outlet port 16.

The first sleeve 48 is fixed within the housing 12, and therefore, hasno axial movement relative to the housing 12. The first sleeve 48 has anarrowed portion 52 which extends immediately from the upper housingwall 18. Additionally, it has an expanded portion 54 which is remotefrom the housing upper wall 18. Inner and outer shoulders 56, 58 are,thereby, defined.

A second sleeve 60 also extends from the upper wall 18 of the housing12. This sleeve 60 encircles, and is generally concentric with respectto, the first sleeve 48. The second sleeve 60, however, is significantlyshorter than the first sleeve 48 for a reason as will be discussednereinafter.

A filter cartridge 62 concentrically encircles the first sleeve 48, anda substantially rigid tubular portion 64 of the filter cartridge 62 aninside diameter substantially the same as the outside diameter of theexpanded portion 54 of the first sleeve 48. Consequently, as the filtercartridge 62 reciprocates axially relative to the first sleeve 48 in afashion as will be discussed hereinafter, the expanded portion 54 of thefirst sleeve 48 functions as a guide for the cartridge 62.

At the same time, the second sleeve 60 also functions as a guide for thefilter cartridge 62. In the case of the second sleeve 60, however,support is exerted radially inwardly upon the cartridge 62 by theencircling second sleeve 60.

A piston surface 66 comprises the upper wall 68 of the filter cartridge62, and the piston surface wall 68 has a central aperture 70therethrough to accommodate the narrowed portion 52 of the first sleeve48. As will be able to be seen then, in view of this disclosure, thenarrowed portion 52 of the first sleeve 48 also serves a guidingfunction for the filter cartridge 62.

The piston surface 66 of the upper wall 68 of the cartridge 62 is sizedand configured so that it completely occludes the annular space 72defined between the second sleeve 60 and the narrowed portion 52 of thefirst sleeve 48, when the filter cartridge 62 is received within thatannular space 72. Consequently, fluid introduced through the inlet port14 will be brought to bear upon the piston surface 66 of the filtercartridge 62 and will drive the filter cartridge 62 downwardly. AnO-ring seal 74 can be carried within a recess 76 formed in the filtercartridge 62 to ensure a seal between the cartridge 62 and the secondsleeve 60 while the cartridge 62 is within the annular space 72.

As seen in the figures, the tubular portion 64 of the filter cartridge62 is provided with a plurality of apertures 78. The apertures 78 arespaced both axially and circumferentially about the member 64.

In the preferred embodiment, the cartridge 62 employs a plurality ofannular supports 80 which space a filter medium 82 radially outwardlyfrom the tubular member 64. The apertures 78 provided in the member 64are disposed so that they underlie the filter medium 82. Consequently,fluid flow through the filter cartridge 62 will be accomplished byallowing passage of the fluid through the apertures 78 and the filtermedium 82.

The filter cartridge 62 is disposed for movement between a primaryposition, illustrated in FIG. 1, and a secondary position, illustratedin FIG. 2. In the preferred embodiment, a coil spring 84 is provided tobias the cartridge 62 to the primary position. As seen in the figures, agenerally annular spring retainer 86 can be carried by the filtercartridge 62 to engage and retain therein an upper end of the coilspring 84. A similar spring retainer 88 can be fixedly carried at adefined axial location along the narrowed portion 52 of the first sleeve48 to engage and retain therewithin the opposite end of the coil spring84.

A valve element 90 is slideably disposed within the narrowed portion 52of the first sleeve 48 for axial movement relative thereto. The valveelement 90, in the preferred embodiment, is sleeve-like inconfiguration.

A diaphragm piston 92 is disposed within the expanded portion 54 of thefirst sleeve 48 for relative movement therewithin. The diaphragm piston92 is, in turn, interconnected to the valve member 90 by a post 94extending axially within the chamber 96 defined by the first sleeve 48.The post 94, as seen in the figures, can be mated to the diaphragmpiston 92 by appropriate threading (as at 98), and to the valve member90 by one or more generally radially extending struts 100. It should bepointed out, however, that, whatever means are employed for mating thepost 94 to the valve member 90, axial fluid flow along the post 94particularly at its axial point of connection to the valve member 90should not be precluded. This is for a reason as will be pointed outhereinafter.

The narrowed portion 52 of the first sleeve 48 includes at least oneorifice 102 formed therethrough. Typically, however, a plurality ofcircumferentially spaced orifices would be provided. In the preferredembodiment, the circumferentially spaced orifices 102 would be at acommon axial location along the narrowed portion 52 of the sleeve 48.

FIG. 1 illustrates the valve member 90 in a primary position thereof.With the valve member 90 in this position, the orifices 102 are occludedto prevent fluid flow therethrough. FIG. 2 illustrates the valve member90 in a secondary position wherein fluid flow through the orifices 102is unobstructed.

A second coil spring 104 is employed for biasing the valve member 90 toits primary position. The primary position is the one the valve member90 would occupy when fluid is not introduced into the filter 10 throughthe inlet port 14. One end of this biasing spring 104 (that is, an upperend) can engage a shoulder 106 defined by a constriction in the passagethrough the narrowed portion 52 of the first sleeve 48. The other endcan engage a shoulder 108 on the inner surface of the narrowed portion52 of the first sleeve 48 at an axial location at which the struts 100mate the valve member 90 to the post 94.

As shown in the figures, the post 94 can be made to extend downwardlyfrom the diaphragm piston 92 to define a scavenger valve spool 110. Thespool 110 includes a primary annular land 112 and a secondary annularland 114. A narrowed diameter portion 116 of the spool 110 is providedbetween the primary and secondary lands 112, 114. Each land is providedwith a diameter such that, when it is axially adjacent the scavengerport 22, it will, in combination with an O-ring seal carried thereby,occlude fluid flow through the scavenger port 22. As the valve element90 traverses from its primary to its secondary position, however, thespool 110 will be moved so that the primary land 112 will becomeunseated from the scavenger port 22 and the secondary land 114 willbecome seated in the scavenger port 22. During the transit, however, thenarrowed diameter portion 116 of the spool 110 will be coextensive withthe port 22, and fluid flow through the port 22 will be permitted.

The figures show the lands 112, 114 as being adjustable axially towardand away from one another. Similarly, the diaphragm piston 92 can beadjusted axially along the post 94. In view of these adjustabilityfeatures, fine tuning of the filter 10 and its scavenger feature can beeffected.

As previously discussed, O-ring seals can be employed at variouslocations as indicated. Additionally, such seals can be included atother interfaces such as the one between the expanded portion 54 of thefirst sleeve 48 and the filter cartridge 62. Such seals, in fact, can beintroduced at any location at which sealing must be effected.

OPERATION

When the filter 10 illustrated in the figures is initially installed,fluid can be introduced through the inlet port 14 to flood the filter10. This will occur as a result of the pressurized fluid driving thefilter cartridge piston surface 66 downwardly to a point at which thepiston surface 66 has escaped the annular space 72 between the secondsleeve 60 and the narrowed portion 52 of the first sleeve 48. This is aposition as seen in FIG. 2. The position of the filter cartridge 62 asseen in FIG. 1 is defined as the primary position, and the position ofthe filter cartridge 62 as illustrated in FIG. 2 is defined as thesecondary position.

As the cartridge 62 moves downwardly and the piston surface 66 thereofmoves axially below the distal end 118 of the second sleeve 60, fluidwill be permitted to flow radially outwardly through an annularescapement slot 120 which will be defined between the piston surface 66of the cartridge 62 and the distal end 118 of the second sleeve 60.Fluid will pass downwardly along the filtration medium 82 and fill thesump 24 in the bottom of the filter housing 12. Once the housing sump 24becomes filled, fluid will pass inwardly through the filtration medium82 and through the apertures 78 in the tubular portion 64 of thecartridge 62. A chamber 122 defined within the tubular portion 64 thenbecomes filled, and pressure will increase within the sump 24 to drivethe diaphragm piston 92 upwardly until it engages the first sleeve innershoulder 56. Once the valve member 90 moves axially relative to thenarrowed portion 52 of the first sleeve 48 to a position at which theorifices 102 become exposed, flow will pass inwardly through thenarrowed portion 52 of the first sleeve 48 and outwardly through theoutlet port 16 in the upper wall 18 of the filter housing 12.

When pressure to the filter 10 is discontinued, the housing 12 willremain flooded. During subsequent operations, particulate materials andother contaminants entrained within the fluid will build up on the outersurface of the filtration medium 82 as fluid passes radially inwardlythrough the medium 82.

As will be able to be seen, however, in view of this disclosure, thetubular member 64 of the filtration cartridge 62, in combination withthe piston surface wall 68 of the cartridge 62 and the outer shoulder 58defined by the first sleeve 48, defines chamber 122 contained by thosemembers. When pressure and introduction of fluid through the inlet port14 have been terminated after a previous operation, the valve member 90will be in its primary position occluding the orifices 102 in thenarrowed portion 52 of the first sleeve 48.

As fluid is reintroduced into the filter 10 through the inlet port 14,therefore, fluid within this chamber 122 will become compressed as aresult of the chamber size being decreased as the filter cartridge 62moves downwardly. The piston wall 68 of the cartridge 62 approaches theouter shoulder 58 defined by the first sleeve 48, and the net volume ofthe chamber 122 is reduced. Consequently, the pressure within thechamber 122 will be increased and will have the effect of purging thefilter medium 82 of contaminants which have become deposited on theouter surface 124 thereof.

As the piston surface 66 is continued to be urged downwardly and thepiston surface 66 passes the distal end 118 of the second sleeve 60, theescapement slot 120 becomes existent, and fluid flows radially outwardlytherethrough. The flow continues downwardly along the filtration mediumsurface 124, and scourging of the surface 124 is accomplished. Thecontaminants, in view of the direction of the flow of the fluid aredeposited within the sump 24.

The increased pressure in the sump 24 will then drive the diaphragmpiston 92 upwardly. The valve member 90 is, commensurately, urgedupwardly to expose the orifices 102 in the narrowed portion 52 of thefirst sleeve 48. As this occurs, normal filtration will occur, fluidflowing radially inwardly through the medium 82, through the apertures78 in the rigid, tubular portion 64 of the filter cartridge 62, throughthe orifices 102 in the narrowed portion 52 of the first sleeve 48, andoutwardly through the outlet port 16. Normal operation will continue aslong as pressurized fluid is introduced at the inlet port 14.

As each new cycle is initiated, as the valve member 90 is drivenupwardly, the primary land 112 will become lifted from its seat at thescavenger port 22. Contaminants in the sump 24 from the immediatelyprevious operation or a number of previous operations will be allowed topass downwardly through the scavenger port 22 as the reduced diameterportion 116 of the spool 110 passes the port 22. Once the secondaryposition of the valve member 90 is achieved, the secondary land 114 willengage and seat at the scavenger port 22 so that pressure within thefilter 10 can be maintained. As will be able to be seen, in view of thisdisclosure, purging of contaminants in the sump 24 can also beaccomplished during movement of the valve member 90 from its secondaryposition back to its primary position, when pressurized fluid isterminated, in view of the narrowed diameter portion 116 of the spool110 passing the scavenger port 22.

As previously mentioned, the axial distance between the lands 112, 114can be varied. Optimum positioning can, thereby, be obtained so thatdesired pressurization of the fluid system can be maintained.

Numerous characteristics and advantages of the invention covered by thisdocument have been set forth in the foregoing description. It will beunderstood, however, that this disclosure is, in many respects, onlyillustrative. Changes may be made in details, particularly in matters ofshape, size, and arrangement of parts witnout exceeding the scope of theinvention. The invention's scope is, of course, defined in the languagein which the appended claims are expressed.

What is claimed is:
 1. A self-cleaning fluid filter, comprising:(a) ahousing having spaced inlet and outlet ports in a common wall thereoffor ingress and egress, respectively, of a pressurized fluid; (b) afirst sleeve, extending from said common wall along an axis of saidhousing, wherein an interior chamber of said first sleeve is in fluidcommunication with said outlet port, said first sleeve having a narrowedportion proximate said outlet port and an expanded portion remote fromsaid outlet port, said narrowed portion of said first sleeve having atleast one orifice formed therein; (c) a second sleeve extending fromsaid common wall and generally concentrically encircling a portion ofsaid narrowed portion of said first sleeve to define a generally annularspace in fluid communication with said inlet port therebetween, saidsecond sleeve having a distal end spaced axially from said expandedportion of said first sleeve; (d) a generally cylindrical filtercartridge encircling said expanded portion of said first sleeve andbeing disposed for telescoping movement, in response to pressurizedfluid flow through said inlet port, relative to said expanded portion ofsaid first sleeve, between a primary position, wherein a piston carriedby a first end of said filter cartridge is received within, andoccludes, said annular space, and a secondary position, wherein saidpiston is outside said annular space and axially intermediate saiddistal end of said second sleeve and said at least one orifice formed insaid narrowed portion of said first sleeve; (e) means for normallybiasing said filter cartridge to said primary position thereof; (f) avalve member received within said narrowed portion of said first sleeveand disposed for telescoping movement relative thereto between a primaryposition, wherein said at least one orifice formed in said narrowedportion of said first sleeve is occluded, and a secondary position,spaced axially from said primary position wherein said at least oneorifice formed in said narrowed portion of said first sleeve isunobstructed; and (g) means, responsive to movement of said filtercartridge, for urging said valve member from said primary positionthereof to said secondary position thereof as fluid flow is introducedthrough said inlet port to urge said filter cartridge from said primaryposition thereof to said secondary position thereof, and for urging saidvalve member from said secondary position thereof to said primaryposition thereof as fluid flow through said inlet port is discontinuedto allow said filter cartridge biasing means to urge said filtercartridge from said secondary position thereof to said primary positionthereof.
 2. A self-cleaning fluid filter in accordance with claim 1further comprising means for normally biasing said valve member to saidprimary position thereof, and wherein said valve member urging meanscomprises;(a) a valve piston, exposed to pressure from fluid enteringsaid inlet port as said filter cartridge is urged toward its secondaryposition and said piston carried by said cartridge passes said distalend of said second sleeve, received within said expanded portion of saidfirst sleeve, said valve piston being operatively connected to saidvalve member for reciprocating movement relative to said first sleeve;and (b) said valve member biasing means.
 3. A self-cleaning filter inaccordance with claim 1 wherein said valve member comprises a thirdsleeve.
 4. A self-cleaning filter in accordance with claim 1 wherein asump is defined within said housing at an end thereof opposite saidcommon wall, and wherein a wall of said housing opposite said commonwall has a scavenger port formed therein.
 5. A self-cleaning filter inaccordance with claim 4 further comprising a spool valve operativelyconnected to said valve member for movement through said scavenger port,said spool valve having primary and secondary annular lands and anarrowed diameter portion interconnecting said lands, said primary andsecondary annular lands each precluding flow of fluid from said housingthrough said scavenger port when said valve member occupies its primaryand secondary positions, respectively, and said narrowed diameterportion permitting flow of fluid from said housing as said valve membertransits between its primary and secondary positions.